Introduction

Gmsh is an automatic 3D finite element grid generator with a built-in CAD engine and post-processor. Its design goal is to provide a simple meshing tool for academic problems with parametric input and advanced visualization capabilities.

Gmsh is developed by Christophe Geuzaine (University of Liège) and Jean-François Remacle (Catholic University of Louvain).

See for all other Gmsh info: http://geuz.org/gmsh/.

Although Gmsh and dolfyn run also on Windows and OS X the walkthru is based on Linux. However everything should work under other operating systems as well.

The convention on these pages is:
red: commands on the command line
blue: the (partial) output of the programs.

Files

Files needed:

NOTE 1: Gmsh 2.4 file format has been silently changed! You may need to edit gmsh2dolfyn.f90 (depending on which Gmsh version you are using). Please ask your questions in the forum.

NOTE 2: gmsh2dolfyn.f90 adapted to Gmsh 2.5.0 (October 2010).

General information on Gmsh and dolfyn

Gmsh is geared towards numerical strength analysis based on the Finite Element Method. This means that "points" and "bars" (1D and 2D elements) are important. Dolfyn however only works with 3D (fluid) cells and uses a separate boundary file (*.bnd). Note that dolfyn cannot use the concept of 2D "shell models". Gmsh' Physical Surfaces are used as dolfyn boundaries.

When the mesh is written by gmsh only "physical entities" are written out the the *.msh file. "Physical Points" and "Physical Lines" are useless to dolfyn and will interfere with the communication from Gmsh to and from dolfyn.

Another issue is that both Gmsh and dolfyn use a *.geo file. The *.geo file for Gmsh contains commands to create a mesh. Dolfyn's preprocessor creates a *.geo file form the geometrical files (*.cel, *.vrt, *.bnd and optionally *.inp). When the preprocessor overwrites the orginal Gmsh *.geo file then it's contents will be lost. One solution is to rename the *.msh file made by Gmsh (see the following tutorials).

Also a newer version of the preprocessor is needed (newer than april 2009). Up until now the preprocessor did not use the order of the boundary definitions in the *.bnd file. The order is important to Gmsh and the interface dolfyn2gmsh.

Of course one can use any output and postprocessor and Gmsh as well. Insert "use gmsh" in the *.din file and a *.msh file with results only will be written. One can ommit the results on the boudaries but then a full *.msh file will be written ("use gmsh fluid"). A full *.msh file containing the mesh, boudaries (including the default boundaries, region 0) will be written with "use gmsh full".

Finally do not forget to compile gmsh2dolfyn.f90.

Contents of the tutorials (showing some of Gmsh' features):

Examples of Gmsh and dolfyn on Windows Vista

vista1

vista2


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